Port config fix to 2.2 (dotnet/extensions#1221)

- port of dotnet/extensions#1202
- with PR tweaks for 2.2
  - e.g. adjust Microsoft.Extensions.Configuration.FunctionalTests.csproj to match layout here
- update PatchConfig.props and NuGetPackageVerifier.json\n\nCommit migrated from dotnet/extensions@9ebff1a

src/Configuration/Config.KeyPerFile/src/KeyPerFileConfigurationProvider.cs

@@ -31,12 +31,13 @@ private static string TrimNewLine(string value)
         /// </summary>
         public override void Load()
         {
-            Data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
+            var data = new Dictionary<string, string>(StringComparer.OrdinalIgnoreCase);
 
             if (Source.FileProvider == null)
             {
                 if (Source.Optional)
                 {
+                    Data = data;
                     return;
                 }
                 else
@@ -63,10 +64,12 @@ public override void Load()
                 {
                     if (Source.IgnoreCondition == null || !Source.IgnoreCondition(file.Name))
                     {
-                        Data.Add(NormalizeKey(file.Name), TrimNewLine(streamReader.ReadToEnd()));
+                        data.Add(NormalizeKey(file.Name), TrimNewLine(streamReader.ReadToEnd()));
                     }
                 }
             }
+
+            Data = data;
         }
     }
 }

src/Configuration/Config.KeyPerFile/test/KeyPerFileTests.cs

@@ -4,6 +4,8 @@
 using System.IO;
 using System.Linq;
 using System.Text;
+using System.Threading;
+using System.Threading.Tasks;
 using Microsoft.Extensions.FileProviders;
 using Microsoft.Extensions.Primitives;
 using Xunit;
@@ -177,6 +179,39 @@ public void CanUnIgnoreDefaultFiles()
             Assert.Equal("SecretValue1", config["ignore.Secret1"]);
             Assert.Equal("SecretValue2", config["Secret2"]);
         }
+
+        [Fact]
+        public void BindingDoesNotThrowIfReloadedDuringBinding()
+        {
+            var testFileProvider = new TestFileProvider(
+                new TestFile("Number", "-2"),
+                new TestFile("Text", "Foo"));
+
+            var config = new ConfigurationBuilder()
+                .AddKeyPerFile(o => o.FileProvider = testFileProvider)
+                .Build();
+
+            MyOptions options = null;
+
+            using (var cts = new CancellationTokenSource(TimeSpan.FromMilliseconds(250)))
+            {
+                _ = Task.Run(() => { while (!cts.IsCancellationRequested) config.Reload(); });
+
+                while (!cts.IsCancellationRequested)
+                {
+                    options = config.Get<MyOptions>();
+                }
+            }
+
+            Assert.Equal(-2, options.Number);
+            Assert.Equal("Foo", options.Text);
+        }
+
+        private sealed class MyOptions
+        {
+            public int Number { get; set; }
+            public string Text { get; set; }
+        }
     }
 
     class TestFileProvider : IFileProvider

src/Configuration/Config.KeyPerFile/test/Microsoft.Extensions.Configuration.KeyPerFile.Tests.csproj

@@ -5,6 +5,7 @@
   </PropertyGroup>
 
   <ItemGroup>
+    <Reference Include="Microsoft.Extensions.Configuration.Binder" />
     <Reference Include="Microsoft.Extensions.Configuration.KeyPerFile" />
   </ItemGroup>